Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

682
FXUS63 KLOT 161746
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
Issued by National Weather Service Detroit/Pontiac MI
1146 AM CST Tue Dec 16 2025

.KEY MESSAGES...

- Moderating temperatures are expected through Thursday.

- Period of rain showers are expected late Wednesday night into
  Thursday, followed by blustery conditions and briefly colder
  conditions Thursday night and Friday.

- More seasonal or above normal temperatures will arrive for
  next week.

&&

.DISCUSSION...
Issued at 223 AM CST Tue Dec 16 2025

Through Wednesday:

Some very isolated, shallow fog/mist remains possible early
this morning west of the Fox valley where temperatures have
fallen locally into the single digits. Low-level moisture
remains confined to a very narrow layer right near the surface,
and incoming cirrus (albeit thin), along with a gradual increase
in the surface flow should continue to mitigate the threat for
dense freezing fog issues.

The surface pressure gradient will gradually tighten today as
deep mid 980s mb surface low scoots across Ontario. This will
yield southwesterly breezes, with gusts around 20-25 mph
expected this afternoon. Dewpoints are forecast to surge into
the upper 20s/near 30 degrees as the low-level flow increases,
and this should help air temperatures push to near to locally
just above freezing under mostly sunny skies. With the increased
moisture blowing across the (diminishing) snowpack across our
south, some minor visibility reductions in mist can`t be ruled
out in spots, but there are no concerns with more widespread fog
at this point this evening.

A shortwave trough will push across the region late this evening
and overnight. Forecast soundings continue to indicate that a
fairly dry sub-cloud layer (under 10 kft) will be in place which
should help curtail much of the precip potential. That said,
the presence of slivers of slightly negative theta-e lapse rates
are indicative of some instability in the 700-500 mb layer, and
recent CAM output shows a decidedly convective look to high-
level reflectivity. Remain somewhat perplexed by the fairly
widespread nature of QPF (0.01 to locally as much as 0.1 inch)
being cranked out by the ECMWF and many of its ensemble members
based on its moisture profiles which don`t saturate meaningfully
under 700 mb. Given the significant sub-cloud dry layer, even
though nearly all of the 925-700 mb layer is above freezing,
wetbulb temperatures are closer to 0 to + 5C, so suppose it`s
not entirely out of the question that convective processes and
sub-cloud evaporation leads to some ice pellets poking through
the dry layer. At this point, have kept PoPs in the 5-10 percent
range as the trough rolls overhead with no mention of precip at
this time.

This shortwave will help send a modest front through the area
into Wednesday morning. This will likely send temperatures
into the 20s near and just after daybreak across the northwest
half of the area. There is some signal in the guidance for post-
frontal stratus development through the afternoon. This is not
ubiquitous however, but if this were to occur, high temperatures
would likely struggle to warm above freezing.

Carlaw


Wednesday Night through Monday:

A deep mid-level trough currently approaching the Pacific
Northwest will track eastward to the western Great Lakes
Wednesday night into Thursday night. A 980 hPa low over western
North Dakota Wednesday evening is progged to gradually weaken
while crossing Lake Superior on Thursday. An elongated 50+ knot
LLJ will spread across the area late Wednesday evening into
Thursday morning, advecting a narrow ribbon of higher low-level
moisture into northern Illinois overnight. Robust low-level
isentropic ascent will promote quick saturation and the
development of drizzle or light rain across much of the area by
sunrise Thursday. While air temps should be several degrees
above freezing before drizzle develops, cannot rule out some
patches of ice on antecedent sub-freezing surfaces. However, air
temps at or above freezing with some sunshine on Wednesday
should limit much of this concern.

Deep moisture aligned with strong height falls and broad mid-
level diffluence will result in a line of rain along an incoming
cold front late Thursday morning into early afternoon. Very
strong ascent and marginal lapse rates throughout much of the
column do suggest a non-zero thunderstorm chance across as least
the far southeast CWA.

Behind the front, temps will begin falling during the
afternoon, with stronger CAA lagging several hours until the
main core of colder air arrives early-to-mid evening. Decent
drying should end the precip behind the front, so while the
forecast does show rain/snow mix mid to late afternoon, it is
more likely that precip quickly ends as rain with the frontal
passage. Later in the evening, steepening low-level lapse rates
with the passing core of cold air combined with marginal
moisture depth will likely result in scattered gusty light snow
showers or flurries for several hours. Otherwise, expect
blustery conditions with post-frontal W/WNW winds gusting over
30 mph to perhaps briefly up to 40 mph through the evening.

A weakening mid-level ridge and associated surface ridge will
cross the forecast area on Friday. A low-amplitude wave will
then cross the Boundary Waters of Minnesota on Saturday while
keeping any appreciable forcing well north of the area. Mostly
sunny skies and developing WAA on Friday should allow temps to
rise into at least the mid 20s. However, temps may continue to
rise through the evening as modest WAA persists amid weak low-
level stability and a 50 knot LLJ spreading over the area. There
is a very low chance (10%) that mid-level snow will saturate to
the surface as far south as the Wisconsin state line during the
evening. Similarly, a narrow ribbon of very light rain may
proceed a passing cold front Saturday afternoon. However, dry
conditions are expected through this period. High pressure will
then cross the region on Sunday, with signals that a mid-level
disturbance embedded in strong WNW flow aloft could bring a
brief period of light snow Sunday night into Monday.

Kluber

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1145 AM CST Tue Dec 16 2025

Ceilings and visibilities remain VFR at midday across the terminals
while patchy high cirrus streams through above 20 kft AGL. Winds
will be the main forecast consideration during the afternoon hours,
amidst south-southwesterly flow with sustained speeds between 10 and
15 knots. Boundary-layer depths improve minimally given the influx
of warm low-level air, but the arrival of stronger flow within the
lowest portion of the column should still support gusts to around 25
knots. The surface gradient decreases slightly after sunset, enough
to present LLWS issues for part of the overnight period. Maintained
inherited wind shear timing/heights, supported by latest modeled sub-
2 kft layer wind trends. An axis of additional mid- and high-based
clouds pass through aloft this evening, but ceilings should largely
hold AOA 15 kft for most of tonight. Still monitoring potential for
MVFR/IFR fog/low-status early Wednesday as skies clear out and
surface dewpoints hold close to air temperatures. Added an
introductory ceiling and visibility line (VFR for now) to serve as a
foundational placeholder for the still marginal potential. Light
northwest winds expected Wednesday afternoon with a period of
SKC.

Kacan

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

Visit us at weather.gov/chicago